1Neuroimaging laboratory,
Department of Radiology, University
of Pittsburgh, Pittsburgh,
PA, United States

The spin-lattice relaxation time in the rotating frame
(T1rho) has been applied in many pathological studies, including cartilage
degradation, cerebral ischemia, and neurodegeneration diseases. Recently, it
has also been reported that the T1rho contrast can detect dynamic changes in
the tissue microenvironment induced by hypercapnia, hyperoxia challenges, or
neuronal activation. T1rho is most sensitive to molecular fluctuations with correlation
times close to the inverse of Rabi frequency of the applied spin-locking (SL)
pulse. Thus, the T1rho relaxation time, measured with different SL
frequencies, which is termed T1rho dispersion, provides valuable information
about the underlying physiological mechanisms. Previous studies have
demonstrated that the chemical exchange between labile protons of proteins
and the bulk water may be an important contributor to T1rho dispersion in
biological tissues in the low-frequency range of below several kHz. In order
to gain more insight about the underlying mechanisms of dynamic T1rho
changes, we investigated the T1rho response during hypercapnia and hyperoxia
for two different SL frequencies.